1. Field of the Invention
The present invention relates to a developing apparatus for use in an image forming apparatus such as a copying apparatus or the like.
2. Description of the Prior Art
An electrostatic latent image developing apparatus is generally provided with a developing sleeve accommodating a plurality of magnets and a toner supply roller having a large number of fine concave portions formed in its surface. Two-component developer consisting of toner and carrier is often employed in this kind of developing apparatus. The toner is supplied from the toner supply roller with respect to the carrier magnetically held on the peripheral surface of the developing sleeve. The toner and the carrier are mixed and stirred on the surface of the developing sleeve so that they may be electrostatically charged with opposite polarity. In this way, the developer is properly adjusted and is then brought into contact with an electrostatic latent image formed on an electrostatic latent image support member so that the charged toner may be electrostatically supplied onto the electrostatic latent image.
In this kind of developing apparatus, the toner is initially supplied onto the developing sleeve in a toner supply region in which the developing sleeve and the toner supply roller confront each other. At this instance, the toner is required to be raised in electrical charge up to a level suitable for the development by bringing it into frictional contact with the carrier satisfactorily, until it is transported into a developing region in which the developing sleeve and the electrostatic latent image support member confront each other.
To this end, a bristle height adjusting member confronting the peripheral surface of the developing sleeve is generally provided on the way from the toner supply region to the developing region. The developer, being transported with the rotation of the developing sleeve, is thus fully mixed and stirred at a location before the bristle height adjusting member.
The height of brush bristles of the developer is adjusted by the bristle height adjusting member. However, the developer, once adjusted in height, is caused to rotate, since it is pushed by other developer being fed thereafter, thus resulting in that the developer once adjusted in height discontinuously comes into contact with that held on the developing sleeve. Consequently, some signs of stirring of the developer appear on the surface of the developing sleeve and result disadvantageously in unevenness of image density.
To steadily obtain the image in nearly fixed density, it is necessary to replenish the toner onto the surface of the developing sleeve by an amount thereof corresponding to that consumed in the developing region. Particularly, in the case where some image having many a solid portion is repeatedly successively copied, a large amount of toner is consumed and the amount of toner to be replenished is therefore relatively large.
However, if the fine concave portions formed in the surface of the toner supply roller are increased in size so that the toner may be completely replenished only in the toner supply region, the toner is excessively supplied in the case of developing the ordinary literal image. As a result, uncharged toner turns into powder and often adheres to the surface of the electrostatic latent image support member to produce fog around the image or to bring contamination inside the apparatus.